Great Britain Philatelic Society

I've had the commercial cover illustrated here for about 20 years -- more or less since it came out of one of the sacks of book club mail that were sorted through by members of the Torquay Philatelic Society. It has a cachet of the Isle of Ulva with a wolf's head in the centre ("ulva" means wolf, according to Wikipedia). The postmark is rather faint -- Isle of Mull in the bottom half, the actual office name at the top is unreadable.

Does anyone know anything about the origin, usage, dates etc of this cachet?